This invention relates generally to friction clutches, and in particular to a clutch assembly that transmits a calibrated amount of centrifugal force.
Friction clutches are widely used in trucks and other automotive vehicles to selectively connect a driving shaft which is a source of rotational power, such as an engine crankshaft, to a driven shaft, such as a transmission input shaft. A typical clutch has a moveable pressure plate connected for rotation with the driving shaft and a friction disk connected for rotation with the driven shaft. When the pressure plate is moved to a position where it clamps the friction disk in operative engagement with a flywheel on the end of the driving shaft, the driven shaft rotates with the flywheel and torque is transmitted from the driving shaft to the driven shaft. When the pressure plate is moved to a position where the friction disk is disengaged from the flywheel, essentially no torque is transmitted and a driver of the vehicle is free to shift gears of the transmission. Existing clutches to which the present invention applies may include multiple pressure plates and friction disks that are compressed by action of the clutch to engage the flywheel and driven shaft.
One or more springs mounted on the cover plate bias the pressure plate to the position where the friction disk engages the flywheel. In one existing design, a conical spring diaphragm is mounted on the cover to exert an axial force on the pressure plate in its extended conical position and to release the pressure plate when flattened by the force applied by a release bearing initiated by depressing the clutch pedal of the vehicle. The spring must be provided with a tension that is sufficiently high to exert adequate pressure on the pressure plate to prevent slipping of the clutch while still permitting ease of disengagement of the clutch through the clutch pedal of the vehicle.
Recent trucks and other automotive vehicles include engines of significantly greater horsepower and torque that require clutches which transmit more power. Each clutch must provide a correspondingly greater plate load to hold the pressure plate in clamped engagement with the friction disk. To facilitate a larger plate load, some clutches include springs of increased size or a greater number of springs (including compression springs) to apply a larger force urging the pressure plate against the friction disk. Unfortunately, these springs can detrimentally increase weight and volume of the clutch. Further, since the driver must oppose a larger spring force when pressing upon the foot pedal, the clutch is more difficult to operate. These clutches are complex, costly, and less reliable. Also, existing centrifugally assisted clutch designs that are known in the art lack a simple retrofit that can be installed on a standard OEM clutch assembly to convert a standard clutch design into a centrifugally assisted clutch.